Unlike most urban forests, Baltimore’s tree canopy is growing — albeit only slightly, according to the U.S. Forest Service.

Foliage covered 28 percent of the city in 2015, 1 percentage point more than it did in 2007. Those estimates are based on aerial images and data gathered using technology known as light detection and ranging surveying, or LiDAR.

The city has been working for more than a decade to meet a goal to grow its tree canopy enough to cover 40 percent of the city, with an original deadline of 2037 that was later moved up to 2030.

Urban foresters said the growth over the past decade is promising, but more effort is needed to meet the goal.

Five of the 32 Kwanzan trees planted by the Catonsville Tree Canopy Project were dead when James Himel,...

“Whether due to human activities or natural events, change in urban tree canopy can be instantaneous and dramatic,” said Erik Dihle, Baltimore’s city forester. “Tree canopy increases resulting from new plantings, natural regeneration and growth are slow processes that take time and commitment.”

A team of researchers from the forest service, the University of Vermont and the city measured changes in the canopy literally tree by tree, unlike other studies that use coarser resolution or calculate estimates based on samples.

They found that 1,300 acres of tree cover were lost from 2007 to 2015, but that 1,500 acres were gained, for a net increase of 200 acres.

That means a total of about 14,500 tree-covered acres — compared to about 21,000 acres that are paved.